Axially contractable actuator

ABSTRACT

An actuator has a first connection point and a second connection point at opposite ends and is contractable along an axis extending between the connection points. The actuator has at least one hollow enclosure with an opening for admitting a pressurized fluid. A simultaneously radially expandable, axially contractable constraining means cooperates with the enclosure. The constraining means converts radial expansion of the actuator into axial contraction when pressurized fluid is admitted into the enclosure. In a preferred form, the constraining means comprises a network of non-stretchable, flexible tension links.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of my co-pending U.S. patentapplication Ser. No. 06/553,530 filed Nov. 21, 1983, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to an axially contractable actuator particularlysuited for robotics applications.

Robotics technology is frequently presented with the problem ofmimicking the function of human hands and arms. Mechanical analogies tohands and arms clearly must include some replacement for the many humanmuscles used to flex and move the human fingers, hands and arms. Whenfluid power, either hydraulic or pneumatic, is used in robotics, a fluidcylinder appears to be a likely substitute for human muscles. However,high pressure fluid requirements due to limited fluid cylinder size andspace and positioning problems complicate the use of fluid cylinders ormake their use impossible for some applications such as inself-propelling walking robots.

Fluid cylinders are also not entirely suitable as actuators in the foodand drug industries. Restrainers must be used to contain dripping causedby leaking seals and misaligned cylinder rods.

SUMMARY OF THE INVENTION

According to the invention, an actuator has first connection means andsecond connection means at opposite first and second ends of theactuator and is contractable along an axis extending between theconnection means. The actuator comprises at least one hollow, enclosurehaving an opening for admitting pressurized fluid. A constraining meanscooperates with the enclosure for converting radial expansion of theactuator into axial contraction when pressurized fluid is admitted intothe enclosure.

The enclosure may be of an elastomeric material.

The constraining means may comprise a network of non-stretchable,flexible tension links.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an actuator, according to an embodiment of theinvention, in a pre-installation state;

FIG. 2 is a side view of the actuator of FIG. 1 in an axiallyuncontracted state after installation on a hinged arm;

FIG. 3 is a fragmentary view of an alternative embodiment having anetwork with six-sided meshes;

FIG. 4 is a side view of the actuator of FIGS. 1 and 2 in an axiallycontracted position after installation;

FIG. 5 is a diagrammatic side view illustrating in simplified form thefunction of the network of the actuator of FIGS. 1-4;

FIGS. 6 to 8 are diagrammatic perspective views illustrating insimplified form the function of the actuator of FIGS. 1-4;

FIG. 9 is a perspective view, partly broken away, of an actuatoraccording to another embodimment of the invention;

FIG. 10 is an exploded perspective view of the actuator of FIG. 9;

FIG. 11 is a perspective view of the friction reducing layer of theactuator of FIGS. 9 and 10;

FIG. 12 is a perspective view of the elastomeric enclosure of theactuator of FIGS. 9 to 11;

FIG. 13 is a sectional view along line 13--13 of FIG. 11;

FIG. 14 is a side view of an actuator according to a further embodimentof the invention in an axially uncontracted state;

FIG. 15 is a side view of the actuator of FIG. 14 in an axiallycontracted state;

FIG. 16 is a sectional view along line 16--16 of FIG. 15; and

FIG. 17 is a sectional view along line 17--17 of FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an actuator 1 according to an embodiment of theinvention. The actuator has a hollow enclosure 2, in this case of anelastomeric material. In other embodiments a plurality of enclosurescould be used together in parallel. The enclosure may be made of rubber,synthetic rubber or a suitable elastomeric plastic material. Theenclosure is closed at a first end 3 where it is bonded about a threadedstud or bolt 4. The stud 4 provides connection means for connecting theactuator to a mounting bracket 8 as seen in FIG. 2. The stud 4 isconnected to the bracket by a pin 10. The mounting bracket is connectedto an articulated arm 39 by a bolt and nut combination 14.

The enclosure has a second end 16 which is open in that it is bondedabout an open ended nipple 18. The nipple has a threaded outer end 22adapted to engage a fitting 24 of a hose 26 as shown in FIG. 4. In thismanner pressurized fluid, such as hydraulic fluid or pressurized air,can be admitted into the open end of the enclosure. The nipple isconnected to a bracket 23 by a nut 25 and thereby comprises a secondconnection means of the actuator. Bracket 23 is mounted on the arm 39 bya nut and bolt combination 27. The bracket and arm serve as an exampleonly of means actuated by the actuator.

The actuator has a network 28 of non-stretchable, flexible tension links30 extending about the enclosure. The links may be, for example,flexible braided wire covered with plastic. A plurality of such wiresare connected together at nodes 32 to form the essentially tubularnetwork. Alternatively the links may be of other materials such as nylontwine. The network has a first end 34. Similarly, the network has asecond end 36. At end 36 the wires comprising the network pass through aplurality of apertures 35 extending through a ring 20 and extendingcircumferentially about the ring. The ring fits over nipple 18 and buttsagainst end 16 of the enclosure. Knots 37 are formed on the ends of thewires to retain the ends of the wires on the ring. In a similar manner,end 34 of the network 28 is connected to ring 6 fitted over stud 4.

In referring to the actuator, axial dimensions and directions extendalong longitudinal axis 38 of FIG. 1 extending between the ends of theenclosure. Transverse dimensions and directions are perpendicular tothis axis.

FIG. 1 illustrates the actuator in its pre-installation or off-the-shelfcondition. The enclosure 2 is unstretched and the network 28 fitsloosely about the enclousre in a bag-like manner. As may be observed,there is considerable space between the network and the enclosure exceptat the ends 34 and 36. It may also be observed from FIGS. 1 and 4 thatthe network has meshes which are larger near the center of the networkto fit the shape of the expanded enclosure. The meshes are progressivelysmaller towards the two ends of the enclosure.

FIG. 2 illustrates the actuator in an extended, initial condition. Inthis case, the enclosure has been axially stretched until the networkfits closely about the enclosure. This is the axially uncontracted stateof the actuator after installation on the arm 39 with a hinged orarticulated joint 41. The initial tension required to maintain thisuncontracted state is provided by a weight 43 connected to a bolt 45 onthe end of the arm.

In order to contract the actuator axially, pressurized fluid is admittedinto the enclosure by hose 26 as illustrated in FIG. 4. The pressurizedfluid admitted into the enclosure causes radial expansion as shown inFIG. 4 where the enclosure bulges most prominently at the midpointbetween its two ends. The network acts as constraining means which is,at the same time, radially expandable, but axially contractable. Thewires or other tension links comprising the network are essentiallynon-stretchable. Consequently the radial expansion of the network,caused by the radial expansion of the enclosure, must be accompanied byaxial contraction of the actuator as may be observed by comparing FIGS.2 and 4.

Since the entire surface area of the actuator is employed in a functionanalogous to a piston in a fluid cylinder, the resultant axial pullingforce is several times larger than the total force exerted by thepressurized fluid acting on a piston inside a fluid cylinder of the samediameter as the actuator.

In the above embodiment there is a tendency for the network to contractaxially faster than the enclosure, resulting in buckling of theenclosure near its two ends as pressurized fluid is introduced. For thisreason, the network has the loose pre-installation state shown inFIG. 1. Providing the initial stretch to the enclosure uponinstallation, as illustrated in FIG. 2, prevents this buckling.

FIGS. 1,2 and 4 illustrate a network comprising four sided meshes. FIG.3 illustrates an alternative embodiment wherein the netowork 28a hasmeshes with six sides when open.

The theory of operation of the actuator 1 is explained with reference toFIGS. 5 to 8. The network is represented by a line 40 of length L inFIG. 5. At one end, the line is attached to a fixed mount 42. At theopposite end, the line is attached to a load 44 slidably resting on asurface 46.

In FIG. 5, a small force FL has been applied perpendicular to the line40. The small force FL produces a tension force FT which is many timeslarger than the force FL for a small angle a. At the same time, the loadis moved a distance D. The relationships are defined by the followingequations: ##EQU1##

FIG. 6 shows an elastomeric tube or enclsure 3 of length L. The tube issealed at both ends, but has a port 5 for admitting a pressurized fluid.The tube is surrounded by eight non-stretchable, flexible tension links7, only three of which can be seen from the illustrated side. At theirfirst ends 9, the links are connected to mount 42. At their second ends11, the links are connected to load 44 slidably resting on a surface 46.

When pressurized fluid is introduced through port 5, a pulling force Fis created due to radial expansion only of the enclosure surrounded bythe links. Referring to FIG. 7, the load 44 has travelled a distance D1due to the radial expansion. Distance D1 is greater than the distance Dof FIG. 5. This is because the links are now deformed into the arc shapeof FIG. 7 rather than the sharp bend of FIG. 5. ##EQU2## whereP=pressure inside enclosure

S=surface area of enclosure

a=angle between centre axis 38 and tangent 41 to a point on enclosuresurface.

If the links are interconnected at regular intervals to form a network13, as seen in FIG. 8, and the enclosure is inflated, a two-foldapplication of the case of FIG. 5 occurs. Firstly, the pressurized fluidinside the enclosure provides a force along the tube's meridians as seenin FIG. 7. Secondly, tension forces TF along equators of the tubeproduce pulling forces PF along the links of the network.

An axially contractable actuator according to the invention offerssignificant advantages over hydraulic or pneumatic cylinders. Theactuator is easier to manufacture and could be considerably lessexpensive than a cylinder. No sealing or leakage problems are likely tooccur because no sliding seals are required as in the case of cylinders.Thus it would be very attractive for installation where fluid leakage isof great concern. The actuator is uneffected by side forces unlike fluidcylinders which cannot tolerate side forces. At the same time, theactuator can be installed more tightly than hydraulic cylinders,allowing more sophisticated robotic arms and hands to be designed.

FIGS. 9 to 12 illustrate an alternative actuator 1.1 which is generallysimilar to actuator 1. Corresponding parts are numbered the same withthe additional designation ".1".

Actuator 1.1 has an enclosure 2.1 which is spindle-shaped in thepre-installation state of FIG. 12. This allows even wall thickness afterexpansion of the enclosure.

Actuator 1.1 also has a network 28.1 of non-stretchable, flexibletension links 30.1 which are embedded in a layer 50 of flexible materialextending about the enclosure. The layer may be of a suitable flexibleplastic, for example. The layer of material is loose and bulgesoutwardly at 52 between the meshes in the pre-installation state. Thispermits the layer 50 to readily stretch to the uncontracted state eventhough the material needn't be elastomeric. This also provides a minimalresistance by the layer 50 against transverse expansion to the axiallycontracted state. At end 36.1 wires comprising the network are placedand bonded inside semicircular channels 35.1 extending along a cylinder20.1. The channels are arranged circumferentially about the cylinder.The cylinder fits over a nipple 18.1 and is bonded to it. Wire 37.1 iswound about cylinder 20.1 and bonded to retain wires of the network onthe cylinder. In a similar manner, end 34.1 of the network 28.1 isconnected to cylinder 6.1 fitted over stud 4.1.

Actuator 1.1 also has a perforated friction reducing layer 54 in thenature of a thin resilient sheet-like tube between the layer 50 and theenclosure 2.1. Layer 54 reduces resistance to expansion caused byfriction between the network 28.1 and the enclosure 2.1 in conjuctionwith layer 50. The perforations 80 eliminate the vacuum that may becreated between layers. A suitable lubricant such as an oil, grease orpetroleum jelly is applied between layer 54 and the enclosure 2.1 tofurther reduce friction. The lubricant may also be applied betweenlayers 50 and 54. Layer 54 has a first end 58 and second end 59. Atfirst end 58 it is fitted over and bonded to a first end 3.1 ofelastomeric enclosure 2.1. Similarly, at second end 59 it is fitted overand bonded to second end 16.1 of the elastomeric enclosure.

Actuator 1.1 may have a longer expected life than actuator 1 due to thereduced friction and consequent reduced wear on the enclosure.

FIGS. 14-17 show an actuator 1.2 according to a further embodiment ofthe invention. This embodiment employs a combined enclosure and network60. The walls 62 are of an elastomeric material, such as rubber andserve as the enclosure. A network 63 of non-stretchable, flexible links64, such as braided wire, are embedded in walls 62. A second network 66of similar or lighter wire, for example, extends across each of themeshes 68 of the network 63. This second network stops undue outwardbulging of enclosure 62 between the wires of network 63.

The actuator 1.2 is similar to previous embodiments, having a port 70for connecting a hose for supplying a pressurized fluid. Rings 74 and 76provide connection means at opposite ends of the actuator. Wires orlinks 64 extend about the rings for added strength as may be seen inFIG. 17. Rings 74 and 76 and links 64 are encapsulated in suitable rigidplastic bodies 75 and 77 at each end of the actuator.

Although an elastomeric material is preferred for the enclosure, othersheet-like, flexible, non-permeable materials of plastic, for example,can be used. Referring to FIG. 9, the entire actuator may comprise thenetwork 28.1 embedded in the non-elastomeric layer 50 which serves asthe enclosure. The connecting means could be of either the form shown inFIG. 9 or the form shown in FIG. 14. The material is oversized and tendsto bulge outwardly between the links of the network. This accommodatesthe necessary expansion and distortion of the enclosure without the needof elastomeric qualities. As used herein the term "network-shapedstructure" refers to embodiments where the network is part of theenclosure, as disclosed in this paragraph, or is embedded in a separatelayer of flexible material, or is a separate component, as disclosedelsewhere herein.

What is claimed is:
 1. An actuator for contracting along an axis from anelongated state to a contracted state, comprising:an impermeableenclosure which is elongated along the axis in the elongated state;means for introducing pressurized fluid into the enclosure; theenclosure having a plurality of closed areas surrounded by at least foursubstantially non-extensible sides which are connected together to forma network-shaped structure, the sides being substantially parallel withthe axis in the elongated state and adjacent connected sides being at asubstantial angle with the axis in the contracted state to enlarge saidareas as the actuator contracts, portions of the enclosure within eachsaid area bulging outwardly, at least in the contracted state, and beingdeformable to permit contraction of the enclosure from the enlongatedstate to the contracted state, the structure having an exterior arclength in the contracted state which is less than the length of thestructure in the elongated state.
 2. An actuator as claimed in claim 1,wherein the enclosure is of an elastomeric material.
 3. An actuator asclaimed in claim 1, wherein the enclosure is of a sheet-like, flexible,non-permeable and non-elastomeric material.
 4. An actuator as claimed inclaim 1, further comprising connection means at opposite ends of theactuator for mounting the actuator.
 5. An actuator as claimed in claim4, wherein portions of the enclosure are non-elastomeric and bulgeoutwardly in the elongated state.
 6. An actuator as claimed in claim 5,wherein the portions of the enclosure are of a flexible material.
 7. Anactuator as claimed in claim 1, wherein the network-shaped structurecomprises a constraining means cooperating with the enclosure forconverting expansion of the actuator transversely to the axis intocontraction along the axis when pressurized fluid is admitted into theenclosure.
 8. An actuator as claimed in claim 7, wherein theconstraining means is simultaneously contractable along the axis andexpandable transversely to the axis.
 9. An actuator as claimed in claim8, where the constraining means extends about the enclosure.
 10. Anactuator as claimed in claim 9, wherein the constraining means istubular, is operatively connected to the enclosure at the ends of theenclosure, and fits closely about the enclosure in an axially elongatedstate.
 11. An actuator as claimed in claim 10, where the non-extensiblesides are connected together at intervals so the constraining meanscomprises meshes with six sides when open.
 12. An actuator as claimed inclaim 10, where the non-extensible sides are connected together atintervals so the constraining means comprises meshes with four sideswhen open.
 13. An actuator as claimed in claim 10, wherein the actuatorhas a pre-installation state where the constraining means fits looselyabout the enclosure, the enclosure being axially stetchable to theelongated state.
 14. An actuator as claimed in claim 10, wherein thenon-extensible sides are longer near the center of the actuator and areprogressively shorter towards the ends of the enclosure.
 15. An actuatoras claimed in claim 10, further comprising a friction reducing layerbetween the constraining means and the enclosure, the friction reducinglayer comprising a tube formed of a resilient, sheet-like material. 16.An actuator as claimed in claim 15, further comprising a lubricantbetween the friction reducing layer and the enclosure.
 17. An actuatoras claimed in claim 10, wherein the constraining means comprises anetwork embedded in a layer of resilient material forming a tubeextending about the enclosure.
 18. An actuator as claimed in claim 17,wherein the layer of resilient material is loose and bulges outwardly inmeshes between the links of the network in the uncontracted state. 19.An actuator as claimed in claim 18, wherein the layer of resilientmaterial comprises the enclosure.
 20. An actuator as claimed in claim10, wherein the enclosure is spindle-shaped in the enlongated state. 21.An actuator as claimed in claim 10, wherein the network is embedded inthe enclosure.
 22. An actuator as claimed in claim 12, furthercomprising additional links extending within meshes of the constrainingmeans for limiting bulging of the enclosure.
 23. An actuator as claimedin claim 15, further comprising a lubricant between the constrainingmeans and the friction reducing layer.
 24. An actuator as claimed inclaim 15, wherein the friction reducing layer is operatively connectedto the enclosure at its ends.
 25. An actuator as claimed in claim 15,wherein the friction reducing layer is perforated.
 26. An actuator asclaimed in claim 7, wherein the constraining means is embedded in theenclosure.
 27. A fluid operated actuator, comprising:(a) expansibleenclosure means having a longitudinal axis, an axially elongated stateand an axially contracted state and including means for admittingpressurized fluid into said enclosure means for shifting said enclosuremeans between said states; and, (b) constraining means disposed aboutsaid enclosure means and comprising a plurality of tension linksconnected together at a plurality of nodes providing a network having aplurality of open mesh areas and each of said mesh areas having at leastfour sides provided by the associated tension links and all tensionlinks of each mesh area are substantially parallel with said axis whenin said elongated state and adjacent connected tension links of eachmesh area are disposed at a substantial angle to each other when in thecontracted state and said enclosure means bulging outwardly through saidmesh areas when in said contracted state.
 28. The actuator of claim 27,wherein:(a) connection means are disposed at opposite ends of saidenclosure means.
 29. The actuator of claim 27, wherein:(a) saidenclosure means is non-elastomeric.
 30. The actuator of claim 27,wherein:(a) said tension links are non-extensible.
 31. The actuator ofclaim 30, wherein:(a) said tension links include wire.
 32. The actuatorof claim 27, wherein:(a) said constraining means are embedded in saidenclosure means.
 33. A fluid operated actuator assembly, comprising:(a)expansible enclosure means having a longitudinal axis, an axiallyelongated state and an axially contracted state and include means foradmitting pressurized fluid into said enclosure means for shifting saidenclosure means between said states; and, (b) constraining meansdisposed about said enclosure means and comprising a plurality oftension links connected together at a plurality of nodes providing anetwork having a plurality of open mesh areas and each of said meshareas having at least four sides defined by the associated tensionlinks, all tension links are generally parallel with said axis when insaid elongated state and adjacent connected tension links are disposedat a substantial angle to each other when in the contracted state sothat the open area of said mesh areas is larger in the contracted statethan in the elongated state and said enclosure means bulging outwardlythrough said mesh areas when in said contracted state.
 34. The system ofclaim 33, wherein:(a) said enclosure means is elastomeric.
 35. Thesystem of claim 33, wherein:(a) said tension links are non-extensible.36. The system of claim 35, wherein:(a) said tension links include wire.37. The system of claim 33, wherein:(a) connection means are secured tosaid constraining means and said enclosure means at the ends thereofpermitting attachment to an item to be moved.
 38. The system of claim33, wherein:(a) said constraining means are embedded in said enclosuremeans.
 39. The system of claim 33, wherein:(a) said enclosure means arenon-elastomeric.
 40. A fluid operated actuator comprising:(a) anexpandable enclosure of a fluid impermeable, flexible, non-elastomericmaterial having an unpressurized, elongated state and including meansfor admitting pressurized fluid into the enclosure for shifting saidenclosure from the unpressurized, elongated state towards a pressurized,contracted state; and (b) a plurality of tension links disposed aboutthe enclosure and connected together at a plurality of nodes to providea network having a plurality of open mesh areas each having at leastfour sides provided by surrounding tension links, the tension linksbeing articulatable about said nodes in response to said shifting of theenclosure, said tension links being substantially aligned in parallelwith said axis when in said unpressurized, elongated state, adjacenttension links being disposed at a substantial angle with each other insaid pressurized, contracted state and portions of said enclosure withineach said open mesh are bulging outwardly from the open mesh areas insaid unpressurized, elongated state to permit said shifting of theenclosure.
 41. An actuator as claimed in claim 40, wherein the tensionlinks are longer between adjacent nodes near the center of the networkand are progressively shorter between the adjacent nodes towards eachend of the network.
 42. An actuator as claimed in claim 41, wherein thetension links are inextensible.
 43. An actuator as claimed in claim 42,wherein the network is embedded in the enclosure.
 44. An actuator asclaimed in claim 43, further comprising connection means secured to thenetwork and the enclosure at the ends thereof for permitting anattachment of something to be moved by the actuator.